1. Field of the Invention
The present invention relates to a thermoplastic resin composition which is excellent in rigidity, impact resistance and flowability and which provides, when molded, molded articles having excellent appearance, in particular, having no noticeable flow marks. In addition, the present invention relates to an injection-molded article comprising the thermoplastic resin composition.
2. Description of the Related Art
Polypropylene-based resins have been used widely in materials required to have rigidity, impact strength and the like. Polypropylene-based resins have recently been used widely, particularly, as materials for automobiles, and especially, ethylene-propylene block copolymers are used increasingly. Although ethylene-propylene block copolymers have conventionally been produced by a solvent method, the ethylene-propylene block copolymers have recently been produced by a continuous gas phase method which comprises a simple production process and by which the ethylene-propylene block copolymer can be produced at low cost.
However, an ethylene-propylene block copolymer produced by the gas phase method has, in general, problems that, due to a lower limiting viscosity [xcex7]EP of an ethylene-propylene copolymer portion, the swelling ratio (SR) is low, flow marks are noticeable and molded articles produced therefrom have poor appearance, and that when the limiting viscosity [xcex7]EP of an ethylene-propylene copolymer portion of the ethylene-propylene block copolymer produced by the gas phase method is increased, pimples are formed and molded articles produced therefrom have poor appearance.
For solving the problems regarding appearance described above, for example, JP-A-07-286022 discloses a propylene-based block copolymer produced by a batchwise solvent method, a n-decane (23xc2x0 C.)-insoluble component of which has a limiting viscosity of 0.1 to 20 dl/g, a n-decane (23xc2x0 C.)-soluble component of which has a limiting viscosity of 5 to 15 dl/g, and from which molded articles can be formed without formation of pimples in their appearance. However, as disclosed in Comparative Example 3 in the foregoing document, an ethylene-propylene block copolymer a n-decane (23xc2x0 C.)-soluble component, which is considered to be an ethylene-propylene block copolymer portion, of which shows a high limiting viscosity contains many rubber granules which will cause pimples.
JP-A-07-286075 discloses a propylene polymer composition comprising a propylene polymer produced in a continuous mode and an ethylene-propylene block copolymer a n-decane (23xc2x0 C.)-soluble component of which shows a limiting viscosity of 5 to 12 dl/g and from which molded articles can be formed without formation of pimples in appearance. However, the amount of the ethylene-propylene block copolymer compounded is as high as 12% by weight or more.
The object of the present invention is to provide a thermoplastic resin composition which is excellent in rigidity, impact resistance and flowability and which provides, when molded, molded articles having excellent appearance, in particular, having no noticeable flow marks, and to provide an injection-molded article comprising the thermoplastic resin composition.
The present invention relates to a thermoplastic resin composition comprising (A) from 35 to 85% by weight of a polypropylene resin, (B) from 10 to 35% by weight of an elastomer (B), (C) from 2 to 30% by weight of an inorganic filler and (D) from 5 to 15% by weight of a resin, wherein the resin (D) has a melt tension (MT), measured at a winding speed of 15.7 m/min, of not less than 0.03 N and less than 0.1 N and a swelling ratio (SR), measured at 220xc2x0 C., an L/D of an orifice of 40 and a shear rate of 1.2xc3x97103 secxe2x88x921, of 1.8 or more, and the time required for the resin (D) until the ratio (G(t)/G(0.02)) of the relaxation elastic modulus G(t) measured at 210xc2x0 C. to the relaxation elastic modulus G(0.02) in a time of 0.02 second reaches 0.01 is not less than 5 seconds and less than 10 seconds.
The present invention also relates to an injection-molded article comprising the above-mentioned thermoplastic resin composition.